(1) Field of the Invention
The present invention relates generally to an autonomous vehicle which runs autonomously on a route of travel toward a destination and its method using a fuzzy control.
(2) Background of the Art
A Japanese Patent Application First Publication (JP-Al) Showa 62-162113 published in Jul. 18, 1987 and Japanese Utility Model Registeration Application First Publication (JP-Al) Heisei 1-15510 published on Oct. 25, 1989 exemplify a previously proposed autonomous vehicle autonomously running on a set route of travel.
A U.S. patent application Ser. No. 337,707 filed on Apr. 13, 1989 also exemplifies the previously proposed autonomous vehicle described above.
It is noted that, in the above-identified Japanese Utility Model Application First Publication No. Heisei 1-15510, a camera which photographs a running route of the vehicle is installed on the autonomous vehicle to run autonomously the vehicle along a guide line, e.g., a white line on the running route of travel.
In addition, in order to smoothly operate the vehicle, the autonomous running vehicle has been proposed in which a concept of fuzzy set is introduced to its steering operation.
The concept of the fuzzy control set in the autonomously running vehicle is such that, using a plurality of control rules defining predetermined controlled variables of the steering operation according to classifications on magnitudes in deviations with respect to a neutral steering position previously divided into such as "large", "intermediate", and "small" and membership functions indicating certainties corresponding to the respective classifications for the actual deviations in terms of fuzzy sets, the steering controlled variable is determined from a total sum of each control rule by correlating the certainties corresponding to respective magnitude classifications for the actual deviations derived by the functions with the control rules.
Hence, according to the aotonomous running vehicle to which the fuzzy control is applied, the vehicle runs autonomously toward a target point which has previously been set on the basis of a map data, a deviation quantity (dispersion) between a predicted value of the steering controlled variable toward, e.g., a constant distance L.sub.m and the automatically set target value is calculated according to a road situation imaged by means of the camera, and an appropriate steering control is carried out by applying the calculated deviation to the above-described control rules.
In more details, the control rules prescribe for each of the plural classifications that a large controlled variable is given to a large deviation, a small controlled variable is given to a small deviation. A degree of importance is increased for the corresponding control rules according to the actual deviation quantity and a weight average is taken for all control rules so that a smooth steering control is carried out.
The control rules and membership functions are set by repeating running simulations for respective running scenes such as straight road run, curved road run, obstacle avoiding run, and turning at intersections.
However, setting operations for the control rules and membership functions are such that the repeated simulations are carried out in a trial and error to approximate the control rules and membership functions. Therefore, a large amount of time is required for the setting operations.
For example, the above-described deviation quantity is represented by the deviation quantity X from both side end portions of the running road and .theta. with respect to the neutral steering angle. In addition, the classifications of magnitudes are divided into three stages: "large", "intermediate", and "small".
Since both of insufficient (-) and extra (+) for "large" and "intermediate" are present, the classifications are divided into five stages. As a total, 25 kinds of control rules will be resulted with both combinations. In addition, since both membership functions of both X and .theta. are respectively defined, these setting operations are extremely troublesome.